When data processing equipment is connected to a telephone system or other analog system, use is made of a modem. The purpose of the modem (modulator/demodulator) is to convert the digital data stream within the data processing equipment into a form which is suitable for transmission over a telephone network, and conversely, to convert analog signals from the telephone system to a form which is suitable for transmission to the data processing equipment. A typical modern modem is disclosed in U.S. Pat. No. 4,431,867.
With the advent of certain advances in modem technology, high speed data transmission has been made possible between computers over a public switched telephone network (PSTN). Furthermore, additional advantages have occurred in the area of portable computing systems. Some of these advantages include small PC card (formerly referred to as PCMCIA) modems that have been developed to offer both high speed data transmission and portability to a mobile user. With such mobile use, it is inevitable that modems will be used in any international country. However, modems intended to be used during international travel must meet all applicable performance, electromagnetic compatibility (EMC), and safety criteria mandated by government controlled regulatory agencies for that country.
A problem arises because there is no single standard telephone line and each telephone network in each country has its own criteria. Each country also has an individual approval procedure, as well as regulations which make it illegal to connect unapproved equipment to the telephone network of that country. Thus, there are two problems which need to be overcome when equipment is connected to a telephone line. First, the equipment must be able to respond to the signals which it received over a particular network and to issue signals which are compatible with that network. Second, the equipment must be approved in a "homologation" process by an appropriate governmental body so that it can be legally connected to the public telephone network. Within this specification, the approval body will be referred to as the PTT (from Postal Telephone and Telegraph) authority. Equipment will not normally be approved by the PTT if it is capable of issuing incorrect signals. Furthermore, the equipment should be tamper proof and, therefore, it should not be possible for some unauthorized person to modify the equipment so that it no longer conforms to the particular network standards.
These problems have resulted in modems which are manufactured in various versions, where each version corresponds to a particular country. For example, a modem requires interface circuitry to provide electrical isolation between the modem's microprocessor-based control circuitry and the higher voltage PSTN network. Such modem interface circuitry is referred to as the Data Access Arrangement (DAA). Normally, the DAA is designed to be country-specific and is intended to be fully compatible with the telecommunications standards mandated by each individual country. In the United States, FCC Standard Part Number 68 governs criteria primarily intended to protect the United States PSTN from damage while connecting to telecommunication terminal equipment (TTE). European agency approval requires that additional telecommunications standards be met. These standards differ significantly from those standards set forth in the United States. Furthermore, some individual European countries have mutually exclusive specifications which often conflict with the standards for other countries. As a consequence, the DAA structure is usually designed to be country-specific. For this reason, modems intended for the world-wide market usually incorporate "pluggable" DAA assemblies which are country-specific, or incorporate a base card design which can be populated with country-specific componentry during manufacturing.
The use of pluggable DAA assemblies and devices which may be modified using country-specific components is expensive and, therefore, is often not economical to implement. Therefore, a need exists for a modem which allows a user to configure a modem to yield telecommunication characteristics suitable for each unique country standard in a manner which is efficient to implement and utilize.